Radon is a naturally-occurring radioactive gas created from the decay of uranium, which is found in rock, soil and water. When radon is created it normally dissipates into the atmosphere. However, buildings can trap radon where it can become concentrated enough to be a health hazard.
Different countries have different guidelines relating to the management of radon. Health Canada's guidelines provide that remedial measures should be undertaken in a dwelling whenever the average annual radon concentration exceeds 200 becquerels per cubic meter (200 Bq/m3) in the normal occupancy area. The US Environmental protection Agency guidelines for maximum exposure are 150 becquerels per cubic meter (150 Bq/m3).
Both the Canadian National Building Code and the US International Building Code have Radon mitigation requirements. Health Canada recommends that the construction of new dwellings should employ techniques that will minimize radon entry and will facilitate post-construction radon removal, should this subsequently prove necessary. One radon reduction method is Active Soil Depressurisation (ASD). ASD involves inserting a pipe through a hole drilled through a basement floor. A fan draws the radon gas from under the floor and pushes it outside.
A radon ventilation system (RVS) can be provided in new construction to prevent buildings from trapping radon. A RVS may be used in homes, apartments or other buildings. A RVS may be made by placing a layer of coarse gravel or perforated pipes underneath the basement slab and withdrawing air from the layer of coarse gravel or perforated pipes.
There are issues with using gravel to create an under-slab airflow layer. Gravel may be in limited supply or prohibitively expensive in the region where the building is being constructed. A gravel layer may not work depending on the gravel supply and installation procedure. Gravel may itself release radon gas. Relying on perforated piping to remove radon is prone to failure as radon may not migrate into the piping.
There is a need for effective, reliable and affordable systems for preventing the buildup of radon gas in dwellings and other buildings.